Use alloantisera against "differentiation antigens" expressed on regulatory T cells to isolate T cell sets with limited and perhaps even unique functional capacities. Define these functional activities (i.e., help, amplification, precursor, suppression) and target cell set on which these activities are expressed. Determine sensitivity of defined sets to thymectomy at various ontogenetic stages and sensitivity to drugs known to influence immune responses. Also check defined sets in terms of memory, specificity and sensitivity to suppression. Recombine isolated sets to define interaction effects; check possibility different helper cells work on different parts of antibody response i.e., amount vs avidity or initiation versus maintenance. Determine mechanisms of communication of sets by looking of Ig-1 linked and H-2 linked collaborative restrictions, production of factors and role of (subsets of) accessory cells in signal transmission. Use data obtained to help understand mechanisms of breaking tolerance, split tolerance produced by altered antigen, antibody feedback, low zone tolerance and mechanism of adjuvant action.